This invention relates to fiber optic beamsplitters and couplers for dividing, combining, and directing light beams along desired pathways.
The use of optical fiber beamsplitter/couplers for directing light along a desired pathway is well known. Various examples of the methods employed to create a network of light pathways have been disclosed, for example, in U.S. Pat. Nos. 4,314,740, 3,968,564, 4,346,961, 4,351,585 and 4,296,995. In each of these patents, however, as well as in other work in this field, at least two optical fibers have been required which are separated by a coupling region, or space, between the fibers and/or the shapes of the fibers must be modified significantly. These prior art arrangements require precise alignment of the fiber ends, which in some cases may be separated by less than a wavelength of light or they require careful juxtaposition of fibers from which portions of the cladding have been accurately removed.
Precise alignment of the optical fiber ends and/or lengths is important also to avoiding polarization shifts. In many applications and uses of optical fibers, it is important to maintain linear polarization of the light. The change of state of polarization could appear as fringe shifts and introduce large noise amplitudes into the readout of, for example, a fiber optic interferometric sensor. To reduce the contribution to the noise amplitude caused by a change of the state of polarization, fiber optic beamsplitters can be made using slanted end, polarization-maintaining fibers. By the use of polarization-maintaining fibers, the contribution of polarization mixing within the fiber is reduced. Precise alignment of the fiber ends and/or lengths can maintain polarization through the coupling region separating two optical fibers.
The precise alignment required of the ends and/or lengths of optical fibers in the coupling region requires very accurate and very time-consuming procedures. The invention described and claimed herein eliminates the problem of aligning two optical fibers in order to transmit light by using an internal slot formed inside an intact optical fiber. This internal slot, instead of the external gaps between fibers, is used to accomplish the redirection and transmission of light along desired pathways.